The conventional reciprocating compressors generally present a hermetic shell, inside which is mounted a motor-compressor assembly in which the compression system presents a cylinder block having one end closed by a cylinder cover, affixed to the cylinder block generally by screws and which directs the gas to a suction chamber, made of a thermal insulating material and which is separated from or installed in the cast block of the compressor. The motor-compressor assembly is housed internally to the compressor shell at a certain distance from the inner wall thereof. Thus, the suction chamber, which has the function of insulating the gas temperature in the cylinder inlet, suffers the action of the inner temperature of the compressor, which temperature, on its turn, tends to be affected by the high temperature of the inner discharge chamber. This type of construction presents a spacing, provided between the relatively cold refrigerant gas being admitted in the suction chamber and the hot gas being discharged and which has a dimension approximately corresponding to the length of the suction chamber, said construction further providing the thermal insulation and, consequently, improving the performance. Other advantage comes from the perfect and reliable sealing between the high and low pressure sides of the compressor, increasing the reliability and reducing leak losses.
However, these conventional constructions are not generally used in refrigeration systems which operate with refrigerant fluid having carbon in its composition, such as CO2, since such systems present operational pressures higher than those obtained with other refrigerant fluids, requiring stronger compressors.
In some of these constructions, the cylinder block defines part of the compressor shell, in which the motor assembly and the compression system of the compressor are mounted. The cylinder block defines, therewithin, a compression cylinder housing a piston which reciprocates in suction and discharge strokes of the refrigerant gas from and to a refrigeration system to which the compressor is associated. The compression cylinder is closed, at one end, by a valve plate onto which is mounted a head generally defining at least one of the suction and discharge chambers of the compressor. In the known constructions, the shell portion incorporating the cylinder block is hermetically closed by one or two end covers, one of which generally defining an oil sump in its interior.
In such constructions, the head affixed to the cylinder block is provided externally to the contour of the shell portion of the compressor, being affixed to the cylinder block by means of screws (WO2005/026548) or by welding.
The systems for fixing the head to the cylinder block, by means of screws, can present, over time, undesired leak of the refrigerant fluid in the form of gas. Since the head in these constructions is external to the contour of the shell portion, the refrigerant gas may leak to the environment in which the compressor is installed, resulting in volume loss of said gas in the refrigeration system.
Besides the possibility of gas leak, the known compressor constructions having the head external to the shell contour present an undesired noise level.
The construction applied to the outer head has the advantage of allowing a better dissipation of the heat generated by the gas compression in the discharge operation of the compressor. However, such known constructions also allows heating the inner parts of the compressor, due to the heat transferred from the head to the parts of said compressor provided adjacent to said head and, in some way, thermally associated with the suction.